Tillerson holds talks in Istanbul amid Turkey-US tensions

US Secretary of State Rex Tillerson was on Sunday holding talks with Turkish leaders in Istanbul in a bid to iron out a series of disputes on issues ranging from Syria to last year's failed coup.

After arriving from the Ukraine, Tillerson met in Istanbul with his Turkish counterpart Mevlut Cavusoglu and was later due to hold talks with President Recep Tayyip Erdogan, officials on both sides said.

Tillerson, the former chief executive of energy giant Exxon Mobil, also addressed the opening ceremony of the World Petroleum Congress in Istanbul, praising the courage of the Turkish people in defending democracy from an attempted coup almost exactly a year ago, although he made no mention of the widespread crackdown that has followed.

"Nearly a year ago, the Turkish people - brave men and women - stood up against coup plotters and defended their democracy," Tillerson said. "I take this moment to recognise their courage and honour the victims of the events of July 15, 2016."

Washington is openly arming the YPG and the group is heavily involved in the US-backed operation to oust IS militants from their stronghold of Raqqa

Turkey's relations with the United States had dropped to a low in the final months of the administration of former President Barack Obama, but Ankara had hoped for a new page under Donald Trump.

Still, it is furious that Trump has continued and even expanded Obama's policy of supporting the Syrian Kurdish People's Protection Units (YPG) as the main fighting force on the ground in Syria against the Islamic State (IS) group.

Ankara considers the YPG a terrorist group and the Syrian branch of the Kurdistan Workers' Party (PKK) that has waged an insurgency inside Turkey since 1984.

But Washington is openly arming the YPG and the group is heavily involved in the US-backed operation to oust IS militants from their stronghold of Raqqa.

Turkey has not ruled out a new cross-border operation in Syria against the YPG, which could spark a dangerous escalation with the US.

Meanwhile, Ankara has achieved no more progress on its aim of extraditing the alleged mastermind of the 15 July failed coup, the US-based preacher Fethullah Gulen.

Gulen denies any link with last year's deadly botched putsch.

Frustrated with the Obama administration's apparent lack of interest in the issue, Turkey hoped for a major shift under Trump but this has yet to materialise.